python - 为什么此 Popen 调用在 Django 2.0 中返回 "io.UnsupportedOperation: fileno"错误？

Question

我最近将我的项目升级到 Django 2.0，然后开始出现错误。首先，每当我启动 django runserver 时，我都会使用 django_gulp 来启动 gulp 进程。我正在使用 runserver_plus branch of the django_gulp project .这是 the relevant code snippet来自 django_gulp 项目，它在那里进行 subprocess.Popen 调用。此调用在 Django 1.11.x 中正常运行。

from __future__ import print_function

import atexit
import os
import psutil
import subprocess
import sys
import traceback

from signal import SIGTERM

from concurrent.futures import ThreadPoolExecutor

from django.core.management.base import CommandError
from django.conf import settings

from django_extensions.management.commands.runserver_plus import Command \
    as DjangoExtensionsRunserverCommand

from env_tools import load_env


class Command(DjangoExtensionsRunserverCommand):
    """
    Subclass the RunserverCommand from Staticfiles to set up our gulp
    environment.
    """

    def __init__(self, *args, **kwargs):
        self.cleanup_closing = False
        self.gulp_process = None

        super(Command, self).__init__(*args, **kwargs)

    @staticmethod
    def gulp_exited_cb(future):
        if future.exception():
            print(traceback.format_exc())

            children = psutil.Process().children(recursive=True)

            for child in children:
                print('>>> Killing pid {}'.format(child.pid))

                child.send_signal(SIGTERM)

            print('>>> Exiting')

            # It would be nice to be able to raise a CommandError or use
            # sys.kill here but neither of those stop the runserver instance
            # since we're in a thread. This method is used in django as well.
            os._exit(1)

    def handle(self, *args, **options):
        try:
            env = load_env()
        except IOError:
            env = {}

        # XXX: In Django 1.8 this changes to:
        # if 'PORT' in env and not options.get('addrport'):
        #     options['addrport'] = env['PORT']

        if 'PORT' in env and not args:
            args = (env['PORT'],)

        # We're subclassing runserver, which spawns threads for its
        # autoreloader with RUN_MAIN set to true, we have to check for
        # this to avoid running gulp twice.
        if not os.getenv('RUN_MAIN', False):
            pool = ThreadPoolExecutor(max_workers=1)

            gulp_thread = pool.submit(self.start_gulp)
            gulp_thread.add_done_callback(self.gulp_exited_cb)

        return super(Command, self).handle(*args, **options)

    def kill_gulp_process(self):
        if self.gulp_process.returncode is not None:
            return

        self.cleanup_closing = True
        self.stdout.write('>>> Closing gulp process')

        self.gulp_process.terminate()

    def start_gulp(self):
        self.stdout.write('>>> Starting gulp')

        gulp_command = getattr(settings, 'GULP_DEVELOP_COMMAND', 'gulp')

        self.gulp_process = subprocess.Popen(
            [gulp_command],
            shell=True,
            stdin=subprocess.PIPE,
            stdout=self.stdout,
            stderr=self.stderr)

        if self.gulp_process.poll() is not None:
            raise CommandError('gulp failed to start')

        self.stdout.write('>>> gulp process on pid {0}'
                          .format(self.gulp_process.pid))

        atexit.register(self.kill_gulp_process)

        self.gulp_process.wait()

        if self.gulp_process.returncode != 0 and not self.cleanup_closing:
            raise CommandError('gulp exited unexpectedly')

请注意 self.stdout 和 self.stderr，subprocess.Popen 的参数，是对 django.core.management.base.OutputWrapper 的引用.目前我能说的就是Django 1.11的OutputWrapper类继承自object，Django 2.0的OutputWrapper类继承自TextIOBase。

这是我遇到的错误:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.6/subprocess.py", line 667, in __init__
    errread, errwrite) = self._get_handles(stdin, stdout, stderr)
  File "/usr/local/lib/python3.6/subprocess.py", line 1184, in _get_handles
    c2pwrite = stdout.fileno()
io.UnsupportedOperation: fileno

如果这是一个 django_gulp 问题，我将在该 repo 中创建一个问题和/或 PR 来解决这个问题。但是，就目前而言，我想让它在我自己的项目中发挥作用。

我还应该提一下，我是在 docker-compose 环境中运行它的，所以可能是某些东西导致了错误。我还没有在非 Docker 环境中对此进行测试。

编辑

根据 this answer ，看来子进程代码可能假设流具有文件描述符，而在这种情况下没有文件描述符。

Answer 1

您看到此错误的原因是类文件对象是 Python 抽象。操作系统和其他进程不知道这个抽象，它们只知道文件描述符。因此，您必须将有效的文件描述符传递给 Popen。

您可以从 _out 访问由 OutputWrapper 包装的流:

self.gulp_process = subprocess.Popen(
    #...
    stdout=self.stdout._out,
    stderr=self.stderr._out)

或者，您可以只为标准输出和错误传递标准文件编号:

self.gulp_process = subprocess.Popen(
    #...
    stdout=1,
    stderr=2)